The mechanism whereby hypoxia elicits a decrease in dopamine content of rat carotid bodies was studied. Hypoxia increases the rate of dopamine release without changing its turnover-rate. Neither the carotid sinus nor the sympathetic nerves participate in the regulation of dopamine content or turnover-rate. The decrease of the dopamine concentration in carotid body elicited by hypoxia was not prevented after transection of the sinus nerve or ganglionectomy. These findings suggest that low arterial pO2 depletes the dopamine stores independently from both types of nerves.